The search for new antibiotics produced by soil microorganisms has encompassed the screening of various genera of bacteria, higher bacteria and fungi including many species within each genus and many strains within each species.
Microorganisms that are receiving increasing attention include the genus Micromonospora, a genus closely resembling Streptomyces but differing in the lack of aerial mycelium and with very narrow hyphae on which minute spores are borne singly.